Grid-Forming Converter With Enhanced Current Limiting Dynamics During Grid Faults and Wide Stability Range

Grid-forming (GFM) converters facilitate voltage and frequency stability in grids with high penetration of inverterbased renewable energy technologies. Under nominal conditions, the primary function of GFM converters is to control the output voltage by operating in voltage-source mode (VSM). During offnominal conditions, especially in the presence of severe grid disturbances, the primary objective is to ensure accurate and fast-response current limiting to protect the GFM converter from overcurrents by operating in current-source mode (CSM). A wide stability margin of the inner loops must be guaranteed in nominal and contingency conditions due to the high variability of scenarios that a GFM converter may encounter. This paper proposes a double-loop controller with current-limiting capability for GFM converters, ensuring good GFM performance in stand-alone and grid-connected scenarios, including those with very weak and stiff grids. Additionally, the proposed controller provides an enhanced current-limiting response with precise current control during faults. Finally, the proposed controller demonstrates a wide stability range in both VSM and CSM modes. This is experimentally validated through tests of GFM performance in very weak and stiff grids, with sudden changes in the short-circuit ratio (SCR), as well as through current-limiting tests under gridvoltage bolted faults conducted across different grid-impedance conditions